Plasma processing is well known as a surface processing method for executing cleaning or etching for an object to be processed such as a board on which electronic parts are mounted. In plasma processing, a board to be processed is put into a vacuum chamber forming a processing chamber. Then, plasma discharge is generated in the processing chamber. When ions and electrons generated as a result of the plasma discharge are made to act on a surface of the board, predetermined surface processing is executed. At the time of the plasma processing described above, particulates, which have been removed when ions and electrons collide with a surface of the object to be processed, are dispersed in the periphery and attached onto an electrode face, on which the object to be processed is mounted, and an inner wall face of a vacuum chamber. The thus dispersed particulates are deposited with the lapse of time.
The attached and deposited foreign objects can be a cause of extending a vacuum exhausting time because they absorb vapor or other gases contained in the atmosphere introduced from the outside each time the vacuum chamber is opened and closed. Further, the plasma processing pressure is changed by the gas discharged from the deposition layer in the process of plasma processing. Therefore, the attached and deposited foreign objects can be a factor to obstruct the maintenance of a proper plasma processing condition. Further, when the foreign objects are attached and deposited in the periphery of the electrode upon which high frequency voltage is impressed, the insulating property is deteriorated by the foreign objects attached to a guide member to guide the electrode and the object to be processed. Accordingly, there is a possibility that an electric discharge is generated from the electrode to a conductive portion in the periphery and the plasma discharge is put into an unstable state. As described above, when the foreign objects are attached and deposited in the vacuum chamber, various problems are caused. Therefore, a conventional plasma processing device is known which has a function of automatically detecting that the foreign objects have been attached in such a manner that the degree of the attachment of the foreign objects does not exceed an allowable limit and also has a function of informing that the maintenance time has come. Concerning this matter, for example, refer to Patent Document 1. In the prior art shown in Patent Document 1, each time vacuum exhausting is executed at the time of operating the device, a period of time in which a predetermined degree of vacuum can be attained is measured and when this period of time has reached a predetermined allowable time, it is decided that the maintenance time has come.
Patent Document 1: JP-A-2002-124503
However, according to the method shown in the prior art described above, unless a considerably large quantity of foreign objects are attached, a remarkable change does not appear in the time in which the pressure reaches a predetermined degree of vacuum. Therefore, it is difficult to accurately judge whether or not it has come to the proper maintenance time necessary for maintaining the device in the best condition.